Controlling method of seat belt retractor

ABSTRACT

In controlling a seat belt retractor, at least one of signals selected from a state signal showing a movement of an occupant wearing a seat belt and an external signal obtained from detecting means installed in a vehicle during running thereof is received. Then, a rotation of a spool for a webbing is controlled by switching a rotational torque of a motor to a predetermined reduction ratio corresponding to at least one of the state signal and the external signal, or a driving state of the motor is controlled to a predetermined torque, to thereby wind the webbing on the spool.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a divisional application of Ser. No. 09/484,450 filed onJan. 18, 2000.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

[0002] The present invention relates to a controlling method of a seatbelt retractor, i.e. motorized seat belt retractor, which can change itsoperating condition to correspond to the state of an occupant wearing aseat belt or to external signals.

[0003] In a seat belt retractor provided in an automobile, it ispreferable to retract an excess amount of a seat belt after the seatbelt is pulled and a tongue is engaged with a buckle device, withoutapplying too much stress to the chest or other portions of an occupantnormally wearing the seat belt.

[0004] Normally used for winding up a seat belt in a seat belt retractoris a biasing force of a single return spring. When a spring providing asmall biasing force is employed in order to reduce stress applied to thechest of an occupant, the force for winding or retracting the seat beltbecomes weak, thus lowering its operation and its accommodation to theretracted state.

[0005] To the contrary, when a spring for providing a large biasingforce is employed in order to provide an enough winding force for itsretraction, the stress to be applied to the chest of the occupantnormally wearing the seat belt is increased.

[0006] Since a single return spring is employed, a conventional seatbelt retractor has a problem that the biasing force of the return springincreases as the amount of withdrawal of the webbing (hereinafter, theterm “webbing” is used for referring to the belt itself in thisspecification) is increased because the return spring is repeatedlywound.

[0007] As one of means for solving the problem with regard to thewinding of a webbing caused by using a single return spring, theapplicant has developed a tension reducing mechanism for reducing theretraction force, which comprises two rope pulleys of truncated coneshape with a helical guide groove (see Japanese Patent No. 2711428).

[0008] On the other hand, the applicant also has developed a seat beltretractor in which a tension control for a seat belt is performed by abuilt-in electric motor to improve comfortableness as one of functionswhen an occupant normally wears, and to correspond to a distance fromanother vehicle running in front of or behind its own vehicle (seeJapanese Unexamined Patent Publication No. H09-132113).

[0009] In the seat belt retractor disclosed in the aforementionedpublication No. H09-132113, an ultrasonic motor is employed as a drivingunit for the tension control and a spring mechanism is provided as amain winding mechanism. The motor is employed for controlling thetension on the seat belt when the occupant wears the seat belt, and forcontrolling the winding and unwinding of the seat belt to correspond toexternal signals inputted during running of the vehicle. Therefore, itis required to rotate the motor in reverse. This makes the controlcircuit complex. Since the operation of winding up the seat belt isperformed by two circuits, there is also a problem that it is hard tosmoothly switch the operation of winding up the seat belt according tothe inputted external signals.

[0010] When the external signals from sensors mounted on the vehicle areset to function as the trigger of the motor, a speed-reduction gear tobe driven by the motor employed in the seat belt retractor can not copewith a wide range of a winding mode because the reduction range allowedby the speed-reduction gear is limited.

[0011] Therefore, it is an object of the present invention to solve theproblems of the prior art and to provide a seat belt retractor in whicha seat belt can be wound by only a motor with a simple control circuitand a driving mechanism, and the winding mode can be set widely tocorrespond to external signals inputted when an occupant wears the seatbelt and a vehicle runs, and to provide a control method for the seatbelt retractor.

[0012] Further objects and advantages of the invention will be apparentfrom the following description of the invention.

SUMMARY OF THE INVENTION

[0013] To solve the aforementioned problems, the present inventionprovides a seat belt retractor comprising: a base frame; a spooljournalled at a spool shaft to the base frame; a speed-reductionmechanism; and a motor for rotating the spool via the speed-reductionmechanism for winding up a webbing onto the outer periphery of thespool. The speed-reduction mechanism has two transmission trains withdifferent reduction gear ratios, switching means for switching thetransmission trains to one of the trains corresponding to a drivingsignal obtained from external units, and resistant torque means having apreset value so that a transmission element common to the two trainstransmits rotation of the motor when the torque of the rotation issmaller than the preset value.

[0014] The driving signal is preferably set according to a state signalobtained by movement of an occupant wearing the seat belt and anexternal signal obtained from detecting means installed in a vehicleduring the running of the vehicle.

[0015] It is preferable that when the state signal is received, therotational torque is reduced at a small reduction gear ratio to besmaller than the preset value of the resistant torque means, and thespool shaft is rotated with the reduced rotational torque for winding upthe webbing.

[0016] It is preferable that when the external signal is received, theswitching means switches the transmission trains so that the rotationaltorque is increased at a large reduction gear ratio to exceed the presetvalue of the resistant torque means to wind the webbing.

[0017] It is preferable in the above that the resistant torque means isa slip mechanism comprising a viscosity resistant element disposed onthe trains of the speed-reduction mechanism.

[0018] It is also preferable that the switching between the trains isachieved by actuating the switching means according to the drivingsignal when the external signal is received and securing a part of thetransmission element disposed in the speed-reduction mechanism.

[0019] It is preferable that the switching means comprises a pawlmechanism which engages one of ratchet teeth formed on the outerperiphery of an internal gear in a planetary gear unit to stop therotation of the internal gear.

[0020] It is also preferable that the switching means comprises a pawlmechanism having two pawls journalled by shafts, which cooperate toengage ratchet teeth of the internal gear to stop rotation of theinternal gear.

[0021] In this case, it is preferable that the two pawls are a firstpawl and a second pawl, and the first pawl pivots about the shaft byexcitation of a solenoid to engage one of the ratchet teeth and, afterthat, the first pawl makes the second pawl to engage another of theratchet teeth.

[0022] It is preferable that a spring connected to the first pawl biasesthe first pawl after cancelling the excitation of the solenoid with theresult that the second pawl disengages from the ratchet teeth.

[0023] It is preferable that the rotation of the spool is reducedthrough a reduction gear train, and the spool shaft is provided with aspool rotation detecting unit for detecting a rotational direction and astopping state of the spool.

[0024] It is preferable that the withdrawal of the webbing is detectedby the start of rotation of the spool and acts as a trigger for turningON a power source of a control circuit for driving the motor.

[0025] The present invention also provides, as another invention, a seatbelt retractor comprising a base frame, a spool journalled at a spoolshaft to the base frame, around which a webbing is wound, a returnspring for winding up the webbing by its return force, and a motor witha speed-reduction mechanism for switching the winding of the webbing,wherein the speed-reduction mechanism has a transmission train with apredetermined reduction gear ratio and switching means for connectingthe transmission train to the spool shaft corresponding to a drivingsignal obtained from an external unit.

[0026] The driving signal is preferably set according to a state signalobtained by movement of an occupant wearing the seat belt and/or anexternal signal obtained from detecting means installed in the vehicleduring running of the vehicle.

[0027] It is preferable that when the external signal is received, theswitching means switches the transmission trains so that the webbing iswound by the return spring at a large reduction ratio.

[0028] It is preferable that the switching of the transmission train isachieved by actuating the switching means according to the drivingsignal when the external signal is received, and securing a part oftransmission elements disposed in the speed-reduction mechanism.

[0029] It is preferable that the switching means comprises a pawlmechanism which engages one of ratchet teeth formed on an outerperiphery of an internal gear in a planetary gear unit to stop therotation of the internal gear.

[0030] The present invention also provides, as a further invention, aseat belt retractor comprising: a base frame; a spool journalled at aspool shaft to the base frame around which a webbing is wound: a returnspring for winding up the webbing by its return force: and a motor witha speed-reduction mechanism for winding up the webbing at a low speedfor fitting the webbing to an occupant, wherein the speed-reductionmechanism has a contrate gear with a predetermined reduction gear ratioand wherein the webbing is wound by driving the motor via the contrategear.

[0031] The present invention also provides, as an invention forefficiently operating the above retractor, a control method of a seatbelt retractor comprising: receiving an external signal outputted tocorrespond to a state signal according to the movement of an occupantwearing a seat belt and/or an external signal from detecting meansinstalled in a vehicle during running of the vehicle; switchingtransmission of a rotational torque of a motor to a predeterminedreduction ratio corresponding to the state signal or the externalsignal, or controlling the driving state of a motor to change its torqueto a predetermined value to control the rotation of a spool; and windingthe webbing onto the spool.

[0032] It is preferable that based on a state signal obtained bydetecting withdrawal of the webbing while the webbing is in the woundstate, the rotation of the motor is stopped.

[0033] It is preferable that based on a state signal obtained bydetecting that a tongue is engaged with a buckle, the motor is drivenwith such torque as to wind the webbing to fit the webbing to theoccupant's body.

[0034] It is preferable that based on a state signal obtained bydetecting that the fitting of the webbing is accomplished, the torque ofthe motor is reduced or the drive of the motor is stopped.

[0035] It is preferable that based on a state signal obtained bydetecting that the withdrawal of the webbing is cancelled, the motor isrestarted to wind the webbing.

[0036] It is preferable that when the withdrawal of the webbing is madeand stopped while a tongue is engaged with a buckle, the winding of thewebbing is started to fit the webbing to the occupant and, after that,the torque of the motor is reduced or the drive of the motor is stopped.

[0037] It is preferable that the torque of the motor for fitting thewebbing to the occupant is set lower than the torque of the motor forfitting the webbing to the occupant just after the tongue is engagedwith the buckle.

[0038] It is preferable that based on a state signal obtained bydetecting that a tongue is disengaged from a buckle, the motor isactivated to wind the webbing into the retractor.

[0039] It is preferable that at the same time of or after apredetermined period of time from the detection of the withdrawal of thewebbing, a power source of a control circuit for operating the motor isturned ON.

[0040] It is preferable that at the same time of detection that thewinding of the webbing is accomplished, or detection that the webbinghas not been withdrawn for a predetermined period of time, a powersource of the control circuit for operating the motor is turned OFF.

[0041] It is preferable that the control method further comprises:switching the torque of the motor to a preset value or a variable valueby switching means according to an obtained external signal to wind thewebbing by the motor.

[0042] It is preferable that the control method further comprises:providing a mode in which the switching means is not returned so as tohold the driving state of the motor after being switched.

[0043] It is preferable that the control method further comprises:providing a mode in which the switching means is not returned so as tohold the driving state of the motor after being switched through torqueresistor means of the speed-reduction mechanism.

[0044] It is preferable that the mode is a holding mode during runningof the vehicle or a child seat fixing mode.

[0045] It is also preferable that the control method further comprises:transmitting a command signal of the motor corresponding to the externalsignal as information to be used for one or all of the seat beltretractors installed in vehicle seats in a communicating method capableof recognizing the seats so as to perform the mode setting for thevehicle seats.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046]FIG. 1 is an exploded perspective view showing components of aseat belt retractor according to an embodiment of the present invention;

[0047]FIG. 2 is an exploded perspective view showing components of aspeed-reduction mechanism of the seat belt retractor of the presentinvention;

[0048]FIG. 3 is a cross-sectional view showing end faces of transmissionelements inside the speed-reduction mechanism;

[0049]FIG. 4 is a cross-sectional view showing sections of transmissionelements inside the speed-reduction mechanism;

[0050]FIG. 5 is an exploded perspective view showing a variation of aretracting mechanism of the seat belt retractor;

[0051]FIG. 6 is an exploded perspective view showing another variationof a retracting mechanism of the seat belt retractor;

[0052]FIG. 7 is an explanatory view schematically showing components forcontrolling mechanisms and units composing the seat belt retractoraccording to the present invention;

[0053]FIG. 8 is an end view showing the structure of a webbingwithdrawal detecting unit and a spool rotation detecting unit;

[0054] FIGS. 9(a)-9(c) are explanatory views schematically showing thestructure and the operation of a first example of a pawl mechanism;

[0055]FIG. 10 is partially exploded perspective view showing a secondembodiment of a structure of a pawl mechanism;

[0056] FIGS. 11(a)-11(d) are explanatory views schematically showing thestructure and operation of the pawl mechanism shown in FIG. 10;

[0057] FIGS. 12(a)-12(c) are explanatory views schematically showingvariations of a switching mechanism of the speed-reduction mechanism;

[0058] FIGS. 13(a) and 13(b) are explanatory views showing the linkagebetween a reduction gear mechanism and a slip mechanism;

[0059] FIGS. 14(a) and 14(b) are explanatory views showing the switchingoperation in a planetary gear unit;

[0060]FIG. 15 is an explanatory view showing a state of withdrawal of awebbing while the webbing is wound;

[0061]FIG. 16 is a flow chart showing the operational flow forcontrolling the winding of the webbing;

[0062]FIG. 17 is a flow chart showing the operational flow for settingeach mode;

[0063]FIG. 18 is a flow chart showing the operational flow forpreventing looseness of the webbing while an occupant wears the seatbelt;

[0064]FIG. 19 is a variation diagram showing a relation among a signalcurrent, unwound amount of the webbing, and tension for winding up thewebbing in each mode of winding the webbing;

[0065]FIG. 20 is a variation diagram showing the controlling state ofthe motor speed corresponding to the withdrawal or retraction of thewebbing;

[0066] FIGS. 21(a)-21(e) are explanatory views schematically showingvariations of the entire structure of the speed-reduction mechanism;

[0067] FIGS. 22(a)-22(c) are explanatory views schematically showingvariations of a first reduction gear mechanism;

[0068] FIGS. 23(a)-23(c) are explanatory views schematically showingvariations of a second reduction gear mechanism;

[0069] FIGS. 24(a) and 24(b) are explanatory views schematically showingvariations of a switching mechanism of the speed-reduction mechanism;

[0070] FIGS. 25(a)-25(d) are explanatory views schematically showingvariations of a slip mechanism;

[0071] FIGS. 26(a)-26(d) are explanatory views schematically showingvariations of the slip mechanism; and

[0072] FIGS. 27(a) and 27(b) are explanatory views schematically showingvariations of a webbing withdrawal detecting unit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0073] Hereinafter, an embodiment of the seat belt retractor and thecontrol method for carrying out the present invention will be describedwith reference to the accompanying drawings.

[0074]FIG. 1 is an exploded perspective view illustrating a schematicstructure of an assembly of the seat belt retractor 1 of the presentinvention including a webbing winding reel 2A; a reel locking mechanism4; a speed-reduction mechanism casing 11 for accommodating a motor 5 asa driving mechanism and a speed-reduction gear mechanism; a planetarygear unit 30 composing a part of the speed-reduction gear 10 (FIG. 2);and detecting units 40 and 50 for controlling the motor. FIG. 2 is anexploded perspective view showing an internal structure of thespeed-reduction mechanism 10 among the components shown in FIG. 1.

[0075] In FIG. 1, the webbing winding reel 2A and the reel lockingmechanism 4 as the known mechanisms are illustrated in the assembledstate. The webbing winding reel 2A comprises a spool 2 on which awebbing W is wound and a base frame 3 rotatably supporting a spool shaft15 of the spool 2, and the reel locking mechanism 4 (only its outerprofile is shown) for preventing the rotation of the spool 2 isintegrally attached to the base frame 3. In this embodiment, a singlevariable speed DC motor 5 is employed as its driving mechanism. Acontrol unit 9 (see FIG. 7) is provided with a circuit device (notshown) in order to control the rotational speed of the DC motor 5. As adriving mechanism to which a rotational torque is transmitted from theDC motor 5, the speed-reduction mechanism 10 is arranged in thespeed-reduction mechanism casing 11.

[0076] The speed-reduction mechanism 10 includes a first reduction gearmechanism or train 10A and a second reduction gear mechanism or train10B so as to have two trains. The operation of rotating the spool 2 isachieved through one train by one of the speed-reduction gearmechanisms. At this point, to prevent rotational torque transmitted fromone driving machine, such as motor, from being transmitted directly tothe two trains, a slip mechanism (hereinafter, designated by numeral 60)as resistant torque means 60 is arranged between gears to slip rotationby a predetermined resistant torque to shut off the transmission of therotational torque through one of the trains. The arrangement of the slipmechanism 60 allows the speed-reduction gear to be switched to havedifferent reduction by switching means 70.

[0077] As shown in FIG. 1, the base frame 3 is a steel product having achannel-like configuration and includes right and left side walls 3 a(not shown) which are provided with supporting holes 3 b (not shown)into which end flanges of the spool 2 are loosely fitted. Formed on aninner periphery 3 c of one of the supporting holes 3 b are teeth (notshown) to which a pawl (not shown) is moved by the locking operation ofthe reel locking mechanism 4 well known so as to engage one of them.This engagement prevents the rotation of the spool 2 when the webbing Wis rapidly withdrawn from the retractor 1 so as to prevent the withdrawnof the webbing. Fixed to the other side wall 3 a of the base frame 3 isthe speed-reduction mechanism casing 11 for housing the assembly of thespeed-reduction mechanism 10 for increasing the rotational torque of themotor 5. The speed-reduction mechanism casing 11 is fixed to the sidewall 3 a through the planetary gear unit 30.

[0078] Attached to the outer end of the speed-reduction mechanism casing11 and the outer end of the reel locking mechanism 4 are a webbingwithdrawal detecting unit 40 and a spool rotation detecting unit 50,respectively. A motor gear 6 is arranged in a lower portion of thespeed-reduction mechanism casing 11 so as to transmit a predeterminedrotational torque to the assembly of the speed-reduction mechanism 10(its structure will be described later). It should be noted that acasing for housing the motor 5 is not illustrated for simplifying thedrawing.

[0079] The structure of the speed-reduction mechanism will be describedwith reference to FIG. 2 through FIG. 4.

[0080] As described above, the speed-reduction mechanism 10 comprisesthe first reduction gear mechanism 10A and the second reduction gearmechanism 10B to compose two trains, which commonly utilize parts of thetransmission elements. In this embodiment, a pawl mechanism driven by anelectric solenoid 71 is employed as the switching means 70 for switchingthe operation of the reduction gear mechanisms.

[0081] The components of the first reduction gear mechanism 10A will bedescribed with reference to FIG. 2 through FIG. 4. FIG. 3 is a sectionalview showing the inside of the seat belt retractor 1 illustrating endfaces of the components (gear) in detail for explaining the engagedstate of the transmission elements of the speed-reduction mechanism 10,and FIG. 4 is a sectional view showing the inside of the seat beltretractor 1 illustrating sections of the components (gears) in detailfor explaining the supporting state of the transmission elements of thereduction gear mechanism 10.

[0082] As shown in FIG. 1 and FIG. 3, the motor 5 is securely fixed to alower end of the base flame after the motor gear 6 is inserted through alower hole 11 a formed in the speed-reduction mechanism casing 11. Themotor gear 6 is engaged with a double gear 12 supported by a rotationalshaft (not shown ) inside the casing 11. Though the double gear 12 iscomposed of two separate gears in FIG. 2, the double gear 12 may beformed integrally. A small gear 12 a of the double gear 12 is engagedwith a reduction gear 13. The reduction gear 13 has a shaft boss 14,which is fitted over a hexagonal bush 16 coaxially integrally formed ona sun gear 31 (the planetary gear unit 30 will be explained later). Thesun gear 31 is loosely fitted over a projection 15 a of the spool shaft15 so that the reduction gear 13 is journalled by the projection 15 a.Formed in the entire side outer surface of the reduction gear 13 is aflat recess 13 a. A rotary damper 17 well known in the art is fixed to aside surface of the recess 13 a. A gear 19 is journalled by a rotorshaft 18 of the rotary damper 17. Oil is sealed within the rotary damper17. A constant resistant torque is applied to the rotor shaft 18 by astructure that a rotor vane (not shown) turns in the oil to developviscosity resistance. Further, housed in the recess 13 a is a spooldriving gear 20, which is fixed to a hexagonal spline 15 b formed at theend of the projection 15 a. The rotation of the spool driving gear 20provides a predetermined rotational torque to the shaft end of the spoolshaft 15.

[0083] The structure of the planetary gear unit 30 arranged coaxiallywith the spool shaft 15 will now be described with reference to FIGS. 1,3 and 4.

[0084] As clearly shown in the exploded perspective view of FIG. 1, theplanetary gear unit 30 comprises two planetary gears 32 which engage thesun gear 31 rotating at the same speed as the reduction gear 13, acarrier 33 which journals the planetary gears 32 and is rotatablecoaxially with the sun gear 31, and an internal gear 34 having internalteeth 37 with which the planetary gears 32 contact and engage. Amongthese components, the carrier 33 has a hexagonal socket 35 on the backsurface thereof. The socket 35 is fitted over a hexagonal large-diameterportion 15 c when the spool shaft 15 is inserted for assembly. Formed onthe entire outer periphery of the internal gear 34 are ratchet teeth 36.The pawl mechanism 70 is engaged with one of the ratchet teeth 36, whichwill be described later. The engagement between the ratchet teeth 36 andthe pawl mechanism 70 fixes the internal teeth 34, so that the rotationinputted from the sun gear 31 is transmitted to the carrier 33 with therevolution of the planetary gears 32 so as to rotate the large-diameterportion 15 c of the spool shaft 15 via the socket 35 at a large speedreducing ratio.

[0085] With reference to FIG. 5, description will now be made as regardto a variation in which a conventional spiral spring as a return springis incorporated in a retractor. In this variation, comparing with thestructure shown in FIG. 2, the return force of the return spring isutilized for rotating the spool shaft in the webbing winding directionin a normal operation. Formed on the end of the projection 15 a of thespool shaft 15 is a cotter 15 d on which a spring bush 101 is fitted. Aninner end 102 a of the return spring 102 as the spiral spring is fixedto the spring bush 101, whereby a torque developed by the winding orunwinding of the return spring 102 is transmitted to the spool shaft 15.A spring cover 103 is fixed to the casing 11 by bolts (not shown) tocover the entire return spring 102. In the seat belt retractorstructured as mentioned above, the webbing is wound up by the returnspring 102 in a normal operation, while the webbing can be wound up bythe motor 5 additionally when the retraction of the seat belt isrequired in running of the vehicle.

[0086]FIG. 6 is a partial perspective view showing parts of thestructure of a variation of the speed-reduction mechanism, in which theaforementioned function for the large reduction gear ratio is omitted toimprove the comfortableness for the occupant wearing the seat belt. Asshown in FIG. 6, the projection 15 a of the spool shaft 15 extendsthrough a boss 110 a of a contrate gear 110 for a large reducing ratiohoused in the casing 11 and fixed to the inner end of the return spring(see FIG. 5). The contrate gear 110 is a large gear on which cone-shapedteeth are formed at a constant pitch. On the other hand, an electricmotor 112 is housed in the casing 11 in such a manner that therotational shaft of the motor 112 and the spool shaft 15 cooperate toform a skew gear to have a right angle or a predetermined inclinationangle. The electric motor 112 is provided at its shaft end with adriving gear 114, which engages the contrate gear 110. The rotation ofthe electric motor 112 is transmitted to the contrate gear 110 withreducing its speed so as to achieve the low speed rotation of the spoolshaft 15. The electric motor 112 is activated when the occupant wearsthe seat belt, whereby the excess amount of the webbing (not shown) iswithdrawn to such an extent not to provide overpressure to the chest ofthe occupant so that the webbing lightly fits the body of occupant. Thewinding of the webbing is performed by the aforementioned return springwhile the vehicle is running. Thus, the omission of the function for thelarge reduction gear ratio enables to manufacture a compact retractor ata low cost.

[0087]FIG. 7 shows a schematic structure of the seat belt retractormentioned above including the respective mechanisms, the control unitfor operating these mechanisms to link with each other, and therespective detecting units and detecting sensors for sending operationalsignals required by the control unit.

[0088] Schematically shown in FIG. 7 are the retractor 1 mentionedabove, the control unit 9 disposed separately from the retractor 1 forperforming a predetermined command operation to the respectivemechanisms housed in the retractor 1 as shown in FIG. 1 through FIG. 4,and external signal sensors for informing the state of the occupantwearing the seat belt and the state of the vehicle with regard to thesafety.

[0089] That is, the spool 2 journalled through the spool shaft 15 to thebase frame 3 is disposed in the retractor 1 so that the webbing W iswound onto the spool 2. The retracting operation of the spool 2 isachieved by the first reduction gear mechanism 10A and the secondreduction gear mechanism 10B as two trains of different reduction gearratios for transmitting the rotational torque of the motor 5, theswitching means 70 for switching between the two trains according to asignal from the control unit 9, the resistant torque means 60 disposedto effect one of the trains through the first reduction gear mechanism10A and the second reduction gear mechanism 10B according to themagnitude of the rotational torque to be transmitted, the webbingwithdrawal detecting unit 40 for detecting the activation of the motoror the rotation of the spool 2 due to the withdrawal of the webbing W,and the spool rotation detecting unit 50. The control unit 9 is disposedto a portion of the vehicle to output an operational signal to the motor5 of the retractor 1. Connected to the control unit 9 through inputs I/F(not shown) are the webbing withdrawal detecting unit 40, the spoolrotation detecting unit 50, a buckle switch 8 built in a buckle 7 toinform that a tongue connected to the webbing engages the buckle, and aplurality of external signal sensors S1 . . . Sn for informing variousstates of the vehicle during running of the vehicle. Therefore, varioussignals indicating various states of the occupant with the seat belt andvarious signals indicating various running states of the vehicle areinputted into the control unit 9. Based on the input signals, thecontrol unit 9 controls ON/OFF of power sources for the CPU and themotor, and/or generates operational signals, such as control signals forthe rotation of the motor and switching signals for switching thespeed-reduction mechanism, to control the operation of the motor by theoperational signals.

[0090] Description will now be made as regard to the structures of thewebbing withdrawal detecting unit 40 and the spool rotation detectingunit 50 with reference to FIG. 8. For explaining the detecting units,FIG. 8 schematically shows two sides of the seat belt retractor 1 wherethe respective detecting units are attached, in a state that the twosides are arranged side by side.

[0091] As shown in the left half of FIG. 8, the webbing withdrawaldetecting unit 40 comprises a switch plate 41 of a fan shape, a pivotpin 42 for journalling the switch plate 41 as a hinge, a contact arm 43extending from the pivot pin 42 for a short length, and a limit switch44 to be turned ON/OFF by the pivotal movement of the contact arm 43.The switch plate 41 is provided with guides 41 a on both ends thereof tolimit the pivotal range (angle) of the switch plate 41. Within thisrange, an arc peripheral edge 41 b contacts a ring-like portion 21 ofthe spool driving gear 20. The switch plate 41 is provided with an arcgroove 41 c inside and along the arc peripheral edge 41 b, so that theperipheral edge 41 b is slightly deformed so as to apply pressure whenthe peripheral edge 41 b is in contact with the ring-like portion 21.Therefore, the switch plate 41 can pivot according to the rotation ofthe ring-like portion 21 without slippage. In FIG. 8, the switch plate41 (shown by two-dot chain lines) pivots in the counter clockwisedirection according to the rotation of the spool 2 in the clockwisedirection (corresponding to the withdrawal of the webbing W), with theresult that the limit switch 44 is turned ON.

[0092] Description will now be made as regard to the operation while thelimit switch 44 of the webbing withdrawal detecting unit 40 is turnedON. In the normal state, in case that the motor is activated by theoperation of the CPU just like this retractor, the ON operation of anignition key of the vehicle may be a trigger for the power source Pw forthe CPU. However, it is most effective that the power source Pw is turnON by the operation of withdrawal of the webbing. This also allows tomake the apparatus compact. The time for tuning ON the power source Pwfor the CPU when the webbing is withdrawn is detected by the webbingwithdrawal detecting unit 40.

[0093] The spool rotation detecting unit 50 is disposed outside the reellocking mechanism 4. The spool rotation detecting unit 50 detects therotational direction of the spool 2, i.e. the direction of withdrawingor winding of the webbing W, and a stopping state of the spool 2. Asshown in FIG. 1 and FIG. 8, the spool rotation detecting unit 50comprises a gear 51 attached on an end of the spool shaft 15 whichrotates coaxially with the spool 2, a train composed of three gears 52for reducing the rotational speed given through the gear 51, and avariable resistor 53 for detecting a value of resistance indicating thefinal rotational angle of the gear 51 obtained after the speedreduction. The rotational state of the spool 2 can be detected bydetecting the variation in voltage obtained through the variableresistor 53.

[0094] The actual operation of the webbing withdrawal detecting unit 40will be briefly explained. When the occupant stops the winding of thewebbing W or withdraws the webbing W while the webbing W is being woundby the operation of the motor 5, the switch plate 41 pivots slightly soas to turn ON the limit switch 44. Therefore, the motor is stopped, sothat the occupant can lightly withdraw the webbing W from the retractor1. As the withdrawal of the webbing W is detected by at least one of thewebbing withdrawal detecting unit 40 and the spool rotation detectingunit 50, the motor is stopped. When the withdrawal of the webbing W isstopped, the motor 5 is turned ON to restart the winding of the webbingW.

[0095] As mentioned above, both the webbing withdrawal detecting unit 40and the spool rotation detecting unit 50 detect the rotation of thespool 2, and the detection functions as the trigger for the circuit. Asshown in FIG. 8, for example, the power source Pw for the CPU may beturned ON by an OR circuit for the detecting units.

[0096] With regard to the pawl mechanism 70 to be engaged with theratchet teeth 36 formed on the outer periphery of the internal gear 34of the planetary gear unit 30, two representative structural exampleswill be explained and variations will be also explained briefly.

[0097] The structure and operation of the pawl mechanism 70 according toa first structural example will now be described with reference to FIG.2 and FIGS. 9(a) through 9(c). The pawl mechanism 70 comprises asolenoid 71 held by the inner surface of the casing 11 and a pivotallever stopper 75. As shown in FIG. 9(a), the solenoid 71 has a plunger72 which slides within the coil thereof by excitation of the solenoid71. The plunger 72 is retracted in the coil when the solenoid 71 is inthe energized state (excited state) and is pulled to its original stateby a spring 73 when the excitation of the solenoid 71 is cancelled.

[0098] The lever stopper 75 journalled by a pivot shaft is disposedadjacent to the plunger 72. The lever stopper 75 comprises a diskportion 75 a coaxial with the pivot, a driving lever 76 and a drivenlever 77, which are formed integrally with the disk portion 75 a to havea predetermined angle therebetween about the pivot shaft. Asillustrated, in the original state, the driving lever 76 is biased bythe spring 73 to have a position such that an end 76 a of the drivinglever 76 extends to the end of the plunger 72. Disposed adjacent to thedriven lever 77 is a pawl 78 which can rotate about a pin formed on thedisk portion 75. In the original state, the pawl 78 is held to be pushedagainst the driven lever 77 by a wire spring 79 fitted around the diskportion 75. The pawl 78 is provided with a releasing projection 78 aformed at the end thereof.

[0099] With reference to FIGS. 9(b) and 9(c), description will now bemade as regard to the operation of the pawl mechanism 70 for engagingthe pawl with the ratchet teeth 36 of the internal gear 34 and forcancelling the engagement.

[0100] There are various modes for winding the webbing W. These modesinclude a mode in which the webbing W is rapidly wound up with a largetorque. The operation of rapidly winding up the webbing W is achieved bytransmitting the rotational torque of the motor 5 through the secondreduction gear mechanism 10B to the spool 2 by the reduced rotation ofthe carrier 33 for the planetary gears 32. Therefore, as mentionedabove, it is required to engage the pawl of the pawl mechanism 70 withthe ratchet teeth 36 formed on the outer periphery of the internal gear34 so as to lock the rotation of the internal gear 34.

[0101]FIG. 9(b) shows the state that the solenoid 71 is excited so thatthe plunger 72 is retracted in the coil of the solenoid 71. With theretraction of the plunger 72, the driving lever 76 of the lever stopper75 is pushed by the end 72 a of the plunger 72 to pivot in the counterclockwise direction. Accordingly, a portion of the pawl 78 projectingfrom the disk portion 75 a and arranged integrally with the driven lever77 is engaged with one valley of the ratchet teeth 36, thereby lockingthe rotation of the internal gear 34 in the clockwise direction. As aresult of this, the planetary gears 32 engaging the internal teeth 37 ofthe internal gear 34 revolves in the clockwise direction with a selfrotation in the counter clockwise direction. The revolution of theplanetary gears 32 makes the carrier 33 to rotate the spool 2 about thespool shaft 15 at a large reduction gear ratio.

[0102] The operation of the lever stopper 75 for cancelling the lockingof the internal gear 34 will now be described.

[0103] As the excitation of the solenoid 71 is cancelled from the statethat the rotation of the internal gear 34 is locked, the plunger 72extends to project from the coil so that the driving lever 76 of thelever stopper 75 pivots in the clockwise direction. At the same time,the driven lever 77 also pivots. Since the pawl 78 is in contact withone of the ratchet teeth 36 with a predetermined pressure at this point,the engagement between the pawl 78 and one of the ratchet teeth 36 isstill held even when the driven lever 77 pivots. As the disk portion 75a further rotates, the pawl 78 pivots toward the driven lever 77 to passover the top of one tooth of the ratchet teeth 36 about the root of theprojection 78 a as its support by means of the return force of the wirespring 79. Therefore, the engagement between the pawl 78 and the ratchetteeth 36 is cancelled.

[0104] The structure and operation of a pawl mechanism 170 according toa second structural example will now be described with reference toFIG.10 and FIGS. 11(a) through 11(d). As shown in FIG. 10 and FIG.11(a), the pawl mechanism 170 comprises a solenoid 171 held by the innersurface of a retainer plate 120, a lever 175 which operates according tothe expansion of a plunger 172 of the solenoid 171, a first pawl 180 tobe engaged at its tip with one of the ratchet teeth 36 by the operationof the lever 175, and a second pawl 182 to be engaged at its tip withone of the ratchet teeth 36 according to the pivotal movement of thefirst pawl 180.

[0105] The solenoid 171 has the plunger 172 which slides within the coilwhen the solenoid 171 is excited. The plunger 172 is retracted in thecoil when the solenoid 171 is in the energized state (excited state) andis extended to its original state by a releasing spring 190 and theoperation of the second pawl when the excitation of the solenoid 171 iscancelled.

[0106] The lever 175 journalled by a pivot shaft 184 is disposedadjacent to the tip of the plunger 172. The lever 175 comprises asupport 175 a coaxial with the pivot shaft 184, a driving lever 176 anda driven lever 177, which are formed integrally with the support 175 ato have a predetermined angle therebetween. As illustrated, the drivinglever 176 has a forked tip 176 a engaging a small-diameter portion 172 aof the plunger 172, so that the driving lever 176 pivots according tothe reciprocation of the plunger 172, with the result that the lever 175turns entirely about the pivot shaft 184.

[0107] The first pawl 180 is positioned below the driven lever 177 insuch a manner that the first pawl 180 is movable along an elongated hole186 by a biasing force of the releasing spring 190. The first pawl 180is substantially formed in an arc shape and is biased in a direction ofan arrow A along the elongated hole 186 by the releasing spring 190connected to the rear end of the first pawl 180. The first pawl 180 isprovided with a notch into which a half at the top of the second pawl182 journalled by a pivot shaft 188 enters.

[0108] With reference to FIGS. 11(b) through 11(d), description will nowbe made as regard to the operation of the pawl mechanism 170 forengaging the pawl with the ratchet teeth 36 of the internal gear 34 andfor cancelling the engagement.

[0109] As in the first structural example, the description will be madeby reference to a case that the webbing W is rapidly wound up with alarge torque. As described above, the operation of rapidly winding upthe webbing W is achieved by transmitting the rotational torque of themotor 5 through the second reduction gear mechanism 10B to the spool 2by the reduced rotation of the carrier 33 for the planetary gears 32.Therefore, as mentioned above, it is required to engage the pawl of thepawl mechanism 170 with the ratchet teeth 36 formed on the outerperiphery of the internal gear 34 so as to lock the rotation of theinternal gear 34.

[0110]FIG. 11(b) shows the state that the solenoid 171 is excited sothat the plunger 172 is retracted in the coil of the solenoid 171. Withthe retraction of the plunger 172, the driving lever 176 of the lever175 is pulled by the end 172 a of the plunger 172 to pivot in thecounter clockwise direction. Accordingly, the driven lever 177 alsopivots about the support 175 a. At this point, the driven lever 177moves the first pawl 180 positioned below the driven lever 177 to pivotin the counter clockwise direction against the biasing force of thereleasing spring 190, thereby engaging a projection 180 a formed on thebottom of the first pawl 180 with one valley of the ratchet teeth 36.

[0111] As shown in FIG. 11(c), as the internal gear 34 rotates about theshaft 15 (the spool shaft) in the clockwise direction, the first pawl180 moves along the elongated hole 186 about the shaft 15 in theclockwise direction in such a manner as to compress the releasing spring190. Since the upper surface of the first pawl 180 is pressed andrestricted by the driven lever 177, the first pawl 180 is prevented frombeing released. At this point, a portion of the notch 180 b of the firstpawl 180 presses the end 182 a of the second pawl 182 so as to move thesecond pawl 182 to pivot about the pivot shaft 188 in the counterclockwise direction, thereby locking the rotation of the internal gear34 in the clockwise direction. As a result of this, the planetary gears32 engaging the internal teeth 37 of the internal gear 34 revolves inthe clockwise direction with a self rotation in the counter clockwisedirection. The revolution of the planetary gears 32 rotates the spool 2about the spool shaft 15 at a large reduction gear ratio.

[0112] With reference to FIG. 11(d), the operation of the lever 175, thefirst pawl 180, and the second pawl 182 for cancelling the locking ofthe internal gear 34 will now be described.

[0113] As the excitation of the solenoid 171 is cancelled from the statethat the rotation of the internal gear 34 is locked, the force forholding the plunger 172 within the coil is cancelled, so that the drivenlever 177 pivots about the pivot shaft 184 in the clockwise directionbecause of the biasing force of the releasing spring 190 in its extendeddirection (direction of arrow A). As a result of this, the force forrestricting and engaging the first pawl 180 with one of the ratchetteeth 36 is cancelled, so that the first pawl 180 pivots about the shaft15 in the counter clockwise direction to bring an end 180 c into contactwith a projection 182 b of the second pawl 182, thereby moving thesecond pawl 182 to pivot about the pivot shaft 188 in the clockwisedirection. In this way, the engagement among the ratchet teeth 36 of theinternal gear 34 and the two pawls 180, 182 can be completely cancelled.

[0114] According to the second structural example described above, it isnot required to rotate the motor in reverse even for cancelling thelocking. The engagement between the two pawls and the ratchet teeth canbe easily cancelled by the two pawls, which is made by means of thebiasing force of the releasing spring.

[0115] Hereinafter, variations of the pawl mechanism 70 according to thefirst structural example will be described in brief.

[0116]FIG. 12(a) shows an example in which the driven lever 77 isdirectly engaged with the ratchet teeth 36. The pawl mechanism 70 ofthis example is provided with a roller R disposed on an end of thedriven lever 77. The rotation of the roller R reduces friction betweenone of the ratchet teeth 36 and the end of the lever 77 so as tofacilitate releasing of the end of the lever 77 from the ratchet teeth36 when the plunger 72 extends, and the driving lever 76 and the drivenlever 77 rotate together in the clockwise direction.

[0117]FIG. 12(b) shows an example comprising a geared motor 91 and anarm-like stopper 92 disposed on the output shaft of the geared motor 91in which the stopper 92 (pawl) is moved to pivot by the operation of thegeared motor 91. FIG. 12(c) shows an example comprising a rack andpinion mechanism 90 in which a rack 90 a is brought into contact withthe ratchet teeth 36 by using a geared motor 91. In cases of FIG. 12(b)and FIG. 12(c), releasing of the stopper (pawl or rack) can be surelyachieved because of using the geared motor.

[0118] With reference to FIG. 13(a) through FIG. 15, description willnow be made as regard to the paths for transmitting the rotational forcethrough the first reduction gear mechanism 10A and the second reductiongear mechanism 10B achieved by the aforementioned mechanisms and to theoperation of the slip mechanism.

[0119] The rotational speed of the DC motor 5 of this embodiment iscontrolled by an open loop method according to pulse signals outputtedfrom a driving circuit. In this embodiment, the control circuit isdesigned to allow the webbing to be wound with a small, middle, or largerotational torque by duty rates of three stages (25%, 50%, 100%). Therelation between the actual using condition and the setting mode forwinding the webbing will be described later.

[0120] First, description will now be made as regard to the operation ofthe respective elements for the transmission of the rotation of themotor 5 to the spool shaft 15 through the first reduction gear mechanism10A for winding the webbing with a small torque.

[0121] As shown in FIG. 13(a), as the motor 5 rotates at a lowrotational speed in the counter clockwise direction for the purpose ofwinding up the webbing, the reduction gear 13 rotates at a lowrotational speed via the gear 12. Since the rotational torque of thereduction gear 13 at this point is lower than the preset torque for therotor shaft 18 of the rotary damper 17 disposed in the recess 13 a, thespool driving gear 20 does not rotate relative to the reduction gear 13and thus rotates together with the reduction gear 13. Therefore, therotational torque of the reduction gear 13 is applied as the rotationalforce for winding up the spool 2 without increase and decrease.According to the rotation of the spool 2, the carrier 33 of theplanetary gear unit 30 integrally attached to the spool 2, the sun gear31 and the internal gear 34 loosely fitted over the projection 15 a ofthe spool shaft 15 do not rotate relative to each other, but rotateintegrally with the spool 2 in the counter clockwise direction (see FIG.14(a)).

[0122] Now, description will be made as regard to the operation of therespective elements for the transmission of the rotation of the motor 5to the spool shaft 15 through the second reduction gear mechanism 10Bfor rapidly winding the webbing W with large torque.

[0123] As shown in FIG. 13(b), as the motor 5 rotates at a highrotational speed in the counter clockwise direction for the purpose ofwinding up the webbing, the reduction gear 13 rotates via the gear 12 ata predetermined reduction gear ratio. The sun gear 31 of the planetarygear unit 30 shown in FIG. 14 (b) rotates to make the same revolution asthe reduction gear 13. Since the pawl of the pawl mechanism 70 isengaged with the ratchet teeth 36 formed on the outer periphery of theinternal gear 34, the rotation of the internal gear 34 is locked.Therefore, the planetary gears 32 revolve with engaging the internalteeth 37 of the locked internal gear 34 according to the self rotationof the sun gear 31, and the carrier 33 journalling the planetary gear 32thus rotates in the counter clockwise directions. According to therotation of the carrier 33, a large rotational torque is transmitted tothe large-diameter portion of the spool shaft 15 through the socket 35.

[0124] Since the rotational torque of the reduction gear 13 at thispoint exceeds the preset torque of the rotor shaft 18 of the rotarydamper 17 provided as the slip mechanism 60, the gear 19 of the rotarydamper 17 engaging the spool driving gear 20 rotates for braking withviscosity resistance. Thus, since the input from the reduction gear 13is shut off by the slip mechanism 60, the rotation of the firstreduction gear mechanism 10A is slipped, thereby preventing the trainthrough the first reduction gear mechanism 10A and the train through thesecond reduction gear mechanism 10B from being connected directly (FIG.13(b)).

[0125] Furthermore, description will now be made as regard to a typicalcondition for activating the slip mechanism 60 with reference to FIG.15. As the occupant clasps the webbing W to stop the winding or towithdraw the webbing W while the motor 5 rotates at a low rotationalspeed, the spool driving gear 20 stops or rotates in the clockwisedirection. At this point, the motor 5 rotates in the counter clockwisedirection. As the rotation of the reduction gear 13 in the counterclockwise direction is stopped, the load is applied in reverse. At thispoint, the spool driving gear 20 with torque exceeding the preset torqueof the rotor shaft 18 of the rotary damper 17 rotates in a directionopposite to the rotational direction of the motor, thus causing slippageto the gear 19 of the rotor shaft 18. Since the withdrawal of thewebbing W is detected by the webbing withdrawal detecting unit 40, theoperation of the motor 5 is stopped, thereby allowing the occupant toeasily withdraw the webbing W.

[0126] Modes in which the motor is driven according to the controlmethod of the seat belt retractor structured as mentioned above will bedescribed with reference to flow charts shown in FIG. 16 through FIG. 18and diagrams showing changes of state when the webbing is wound shown inFIG. 19 and FIG. 20.

[0127]FIG. 16 is a flow chart showing the operational flow forcontrolling the winding of the webbing. FIG. 17 is a flow chart showingthe processing flow for setting the modes. FIG. 18 is a flow chartshowing the operational flow for improving the comfortableness for theoccupant wearing the seat belt.

[0128] As described above, the speed of the DC motor 5 used in the seatbelt retractor 1 can be set in detail by setting a voltage or settingpulse signals in the control circuit. Therefore, the operational modefor winding the webbing can be suitably set to correspond to movement ofthe occupant wearing the seat belt and various external signals receivedduring movement of the vehicle, thereby achieving the minute windingoperation of the seat belt.

[0129] The operations in each mode corresponding to the state signalfrom a point when the occupant wears the seat belt after getting on thevehicle to a point when the occupant takes off the seat belt for gettingoff the vehicle, and to the external signal obtained during running ofthe vehicle will be described in connection with the setting of therotational speed of the motor.

[0130] At the same time that the occupant sits on a vehicle seat, theoccupant normally pulls out the seat belt and inserts the tongue intothe buckle at a side of the seat opposite to the side where theretractor is positioned. At this point, the withdrawal of the webbing Wis detected by the webbing withdrawal detecting unit 40 of the retractor1 so as to turn ON the power source Pw for the circuit and CPU (Step100, Step 110). The power source Pw may be turned ON according to anexternal signal by the activation of the ignition key or the like. Bythe state signal indicating the detection of the webbing withdrawal, theoperation of the motor 5 is stopped so as to cancel the winding of thewebbing (Step 120, Step 130). After that, when the tongue is correctlyengaged with the buckle and thus the buckle switch 8 (see FIG. 7) builtin the buckle 7 is turned ON, the motor 5 rotates at a middle speed forwinding up the webbing W in order to remove the excess amount of theseat belt to fit the seat belt to the occupant. This allows the webbingW to extend on the chest to the waist of the occupant withoutoverpressure. As a result of this, slack of the webbing can beeliminated, so that the seat belt can be lightly fitted to theoccupant's body (Step 150). According to a state signal indicating thatthe fitting of the webbing is achieved, the torque of the motor may bereduced or the operation of the motor may be stopped to eliminate thefeeling of pressure to the occupant. When the occupant moves largelyforward from the state mentioned above, the webbing is withdrawnaccording to this movement. After a point when the withdrawal of thewebbing is stopped, the winding of the webbing is restarted in the samemanner.

[0131] When a state signal indicating that the withdrawal of the webbingW is stopped in a middle thereof is inputted, the webbing W is wound upat a predetermined torque to be housed in the retractor 1 (Step 125,Step 145).

[0132] As the occupant bends forward when the tongue is engaged with thebuckle, the webbing is further withdrawn. At this point, the operationof the motor 5 is stopped. When the occupant stops bending and returns,a state signal indicating that the withdrawal of the webbing is stoppedis inputted. According to the state signal, the motor is activated torestart the winding of the webbing. After the webbing is lightly fitted,the driving torque of the motor may be reduced or the operation of themotor may be stopped.

[0133] When the occupant is about to get off the vehicle, the webbing Wis required to be wound up slowly after the tongue is disengaged and tobe stored into the retractor within a pillar or the like for apredetermined amount. After that, when it is determined that thewithdrawal is not performed for a predetermined period, the power sourcePw for CPU is turned OFF by the circuit (Step 170 through Step 195).

[0134] In this manner, the comfortableness when the occupant puts on theseat belt is improved. To further improve the comfortableness when theoccupant wears the seat belt, it is preferable to control the retractorto perform movements as described below. The description will be madewith reference to FIG. 18 and FIG. 20.

[0135] Conventionally, when the occupant slides the seat backward bymeans of a seat sliding mechanism or the like after wearing the seatbelt, the withdrawal of the seat belt is not detected. To cope with sucha situation, the winding of the seat belt is repeatedly performed atpredetermined intervals, thereby cancelling the looseness of the seatbelt when wearing. Concretely, as shown in FIG. 18, when the withdrawalof the seat belt is detected, the predetermined winding is performed(Step 300, Step 310). When a predetermined time period passes after thewinding is completed (Step 320, Step 330), the winding is started again(Step 310) and whether the winding is enough is detected from thewebbing state (S340). When the winding is enough, the winding iscompleted (Step 350). This detecting loop is repeatedly performed atpredetermined intervals. In this way, the looseness of the webbing canbe completely cancelled while the occupant wears the seat belt.

[0136] In the present invention, the webbing can be wound by the motorfor fitting the webbing to the occupant. At this point, the pressure onthe chest of the occupant can be softened by controlling the speed ofthe motor. Concretely, the motor is set to have various speeds as shownin FIG. 20. The speed of the motor may be controlled by a known method,such as controlling PWM driving or controlling operational voltage. Thespeed control can be performed at predetermined intervals (for example,1 minute). In this speed control, the driving of the motor is stopped toreduce the tension on the seat belt for the purpose of facilitating thewithdrawal of the seat belt before the tongue is engaged with the buckleas shown in the variation diagram of FIG. 20. On the other hand, sinceit is preferable to quickly wind up the webbing immediately after thetongue is engaged with the buckle, the rise in speed of the motor atthis point is set to be the same as a conventional one.

[0137] During running of the vehicle, the motor is controlled mainlyaccording to pulse signals corresponding to detected external signals.The motor can be set in one of the following modes according to thestate of emergency.

[0138] Warning Mode

[0139] The main object of this mode is to inform an emergent situationto the driver, for example, when a distance detecting sensor detectsthat the distance from another vehicle in front of or behind the ownvehicle is shorter than the preset value. The preset value for thedistance from another vehicle can be variously set, for example,according to the vehicle speed. For example, when there is an objectwithin a predetermined distance, the webbing is wound in order to informthe presence of the object and the approaching state to the driver. Itshould be considered that the motor may be prevented from being set inthe warning mode when the vehicle is brought closer to an objectintentionally by the driver, such as for moving the vehicle into agarage, by using a speed of the vehicle, a relative speed to the object,a rate of change, and the like as factors.

[0140] Holding Mode

[0141] The object of this mode is to hold the occupant's body by windingup the webbing, for a more emergent situation than that of the warningmode. For example, when the driver dozes during driving so that thedriver bents forward while withdrawing the seat belt and a conventionaldoze detecting sensor detects the doze of the driver, the winding of thewebbing by the motor in this mode functions as an alarm forstraightening the driver's posture and waking up the driver. When thevehicle runs on a bad road, a signal for activating the motor in thismode may be outputted to improve the safety by holding the driver and/oroccupant to the seat. In this case, as a trigger for outputting anexternal signal for this mode, an ABS operational signal and signalsfrom a steering angle sensor and a road surface sensor may be employed.

[0142] Pretensioning Mode

[0143] Conventionally, a seat belt device is equipped with apretensioner for winding up a predetermined amount of webbing when avehicle collision or emergency deceleration is detected, therebyimproving the effect of restraint of an occupant. When it is determinedby a distance detecting sensor, such as a laser radar, that it isimpossible to escape from a vehicle collision, the webbing is rapidlywound up by the motor prior to the collision. The speed of winding upthe webbing should be set not to harm the occupant due to the rapidwinding to prevent the secondary accident.

[0144] In Case of Fixing a Child Seat

[0145] A child seat is normally fixed to a seat by means of a webbing.As for a conventional child seat, it is required to withdraw the entirelength of the webbing to fix the child seat to the vehicle seat forpreventing looseness during running of a vehicle. Accordingly, it isdesired to provide a dedicated mode to fix the child seat to the vehicleseat. For example, a child seat switch is provided. When the switch isturned ON, the webbing is tightly wound until the child seat is fixed tothe vehicle seat with a relatively large torque.

[0146]FIG. 17 is a flow chart showing processes for the respectivemodes. As a signal of setting one of the modes is inputted to thecontrol circuit from an external sensor or the like during running ofthe vehicle or while the child seat is fixed, the speed and/or the timeperiod for winding up the webbing is set corresponding to the mode (Step310, Step 320, Step 330). For switching the speed-reduction mechanism10, the train change is started (solenoid of the pawl mechanism 70 isexcited), so that the rotational torque of the motor is transmitted tothe spool 2 through the second reduction gear mechanism 10B (Step 340).The winding of the webbing W is performed in the mode (Step 350). Incase a signal for cancelling the aforementioned mode or a signalindicating that the safety is ensured is inputted, the train change isfinished (Step 370).

[0147] As the child seat switch is turned ON for mounting the childseat, the train change is started to wind up the webbing W for apredetermined period (Step 400 to Step 420). In case of taking off thechild seat, the buckle switch is turned OFF when the tongue isdisengaged from the buckle (Step 430). The train change is finished(Step 370) when it is detected that the buckle switch is turned OFF, sothat the mode is returned to the comfort mode of slowly winding thewebbing.

[0148] In the hold mode or in the warning mode, the speed of the motoris preferably set to provide a medium rotational torque. In thepretensioning mode, the speed of the motor is preferably set to providea large rotational torque.

[0149]FIG. 19 is a variation diagram indicating conditions for windingthe webbing, schematically showing the relation among the signal currentfor driving the motor for winding the webbing, the withdrawing amount ofthe webbing, and the tension for winding up the webbing into theretractor, which are measured to be fed back to the control circuit. Theabscissa of this diagram indicates elapsed time (t) which is scaled forroughly showing the elapsed time relative to the movement of theoccupant and to the state of the vehicle. Among the curves in thediagram, a signal current curve indicates the state of driving of themotor, a withdrawing amount curve indicates the movement of the webbingwithdrawn from the retractor, and a tension curve indicates a pullingforce by the occupant and a winding force by the operation of the motor.As apparent from the diagram, the operation of the motor is controlledaccording to the state of the webbing withdrawn from the retractor,thereby suitably controlling the tension of the webbing.

[0150] Hereinafter, variations of the entire structure and therespective components of the speed-reduction mechanism 10 will bedescribed.

[0151]FIG. 21(a) through FIG. 21(e) are schematic explanatory viewsshowing variations of the entire structure of the speed-reductionmechanism 10.

[0152] In FIG. 21(a), the first reduction gear mechanism 10A and thesecond reduction gear mechanism 10B are separately disposed and thetransmission of the rotational torque of the motor 5 is allowed to beswitched by shifting the switch gear 70. The shift of the switch gear 70is achieved by sliding its shaft or moving the switch gear 70 along theshaft. In this case, since the slip mechanism 60 does not effect thesecond reduction gear mechanism 10B, a large rotational torque can beeffectively outputted. The switching between the train through the slipmechanism 60 and the train through the second gear mechanism 10B fortransmitting the rotational torque of the motor 5 may be performed bythe operation of a solenoid 71 as shown in FIG. 21(b) instead of theswitch gear. FIG. 21(c) shows a variation in which the switch gear 70 isdisposed between the second reduction gear mechanism 10B and the slipmechanism 60. As shown in FIG. 21(d), the switching of the train for themotor may be performed directly between the first reduction gearmechanism 10A and the second reduction gear mechanism 10B and theconnection between the spool 2 and the slip mechanism 60 can beestablished or cut by the solenoid 71.

[0153]FIG. 21(e) shows a variation of the speed-reduction mechanismcomprising a single train in which the rotational torque of the motor 5is transmitted to the spool 2 through the first reduction gear mechanism10A and the slip mechanism 60. Because in this mechanism, weight isgiven to the operation ability in the comfort mode, it is preferablethat the operation of winding up the webbing with a large torque in theevent of emergency is performed by other biasing means.

[0154] FIGS. 22(a) through 22(c) are schematic explanatory views showingvariations of the first reduction gear mechanism 10A. On the basis ofits function for securely transmitting the rotational torque from theshaft of the motor to the output shaft 25, such as a shaft for windingup the webbing, a pulley 6P is disposed to oppose the shaft of the motorto transmit the torque of the motor to the output shaft 25 of thespeed-reduction mechanism through a transmitting belt 22 (see FIG.22(a)).

[0155] Employed as the transmitting belt 22 include a timing belt, beltshaving various section (V, plane), a resin wire, a steel wire, a chainand the like.

[0156] As a speed-reduction mechanism, a planetary gear unit 23 may beemployed. In this case, a planetary gear side (carrier 23 a) forsupporting the planetary gears or internal teeth of an internal gear 23b is an input shaft, so that the torque from the input shaft can betransmitted to the output shaft 25 (see FIGS. 22(b), 22(c)).

[0157] The mechanism for switching from the train through the firstreduction gear mechanism to the train through the second reduction gearmechanism to obtain large torque will be described. FIG. 23(a) shows avariation in which the carrier of the planetary gear unit 23 is lockedso as to output the input from the sun gear to the output shaft throughthe internal teeth of the internal gear 23 b. FIGS. 23(b) and 23(c) showa variation in which the transmission from the input 24 to the output 25coaxially arranged is achieved by an intermediate gear 26. Theintermediate gear 26 can be shifted by a clutching operation. The inputshaft 24 and the output shaft 25 may be arranged to have different axesto compose a gear train through the intermediate gear 26.

[0158] FIGS. 24(a) and 24(b) show examples of a magnetic-particle clutchin which magnetic particles 95 are filled in a space between theinternal gear 34 and a flange 93, which has substantially the samediameter as the internal gear 34 and is disposed adjacent to theinternal gear 34, and an electromagnetic coil 94 is guided by the flange93 to be wound therearound. In this magnetic-particle clutch, the coil94 is excited to make the magnetic particles in the solid state, therebylocking the rotation of the internal gear 34. FIG. 24(a) shows anexample in which the magnetic-particle clutch is arranged along a sidesurface of the internal gear 34, and FIG. 24(b) shows an example inwhich the magnetic-particle clutch is arranged along the outer peripheryof the internal gear 34.

[0159] Now, a variation of the slip mechanism 60 will be described.Though the slip mechanism 60 using the rotary damper 17 is employed inthis embodiment, variations using a frictional mechanism or a springbiasing mechanism as a torque limiter may also be employed. FIG. 25(a)shows a slip mechanism 60 in which disks are prevented from rotatingwith a torque less than a predetermined torque by a plate spring 63. Theplate spring 63 is attached to a flange of an inner disk 61 and isprovided with a brake pad 64 attached to its end. The brake pad 64presses a flange 62 a of an outer disk 62 so as to apply slideresistance. Therefore, the inner and outer disks 61, 62 rotate togetheruntil the torque of the outer disk 62 exceeds a predetermined value.FIG. 25(b) shows a variation in which a ring-like vane 66 is provided onthe outer periphery of the inner disk 61. The outer disk 62 has aring-like oil chamber 65 in which silicone oil is sealed, and thering-like vane 66 is arranged coaxially with the outer disk 62. In thiscase, also, the inner and outer disks 61, 62 rotate together until theviscosity resistance developed by the vane and oil around it exceeds apredetermined value.

[0160] As shown in FIG. 25(c), a slip mechanism 60 may be arranged andformed as an outer ring, and a spiral spring 67 is arranged to becompressed within an inner space of the slip mechanism 60. With thisstructure, a rotational torque by the biasing force of the spiral spring67 is transmitted to an outer ring 62 until exceeding a predeterminedtorque. After exceeding the predetermined torque, the slip mechanism 60shuts off the rotational torque developed by the biasing force. As shownin FIG. 25(d), instead of the spiral spring 67, a compressed spring coil67 may be employed to exhibit its biasing force according to apredetermined rotational angle.

[0161] FIGS. 26(a) through 26(d) show examples of a slip mechanism 60disposed between an outer disk 62 and an inner bush 61 arrangedcoaxially with the outer disk 62. In the slip mechanism 60 shown in FIG.26(a), the outer disk 62 is provided with a transfer curve 62 bcorresponding to ¼ circle and a step portion 62 a on the inner peripherythereof, and a steel ball 68 is housed at the terminal end of thetransfer curve 62 b. The inner bush 61 is provided with a radiallyextending notch in which a spring S is placed. By the spring S, thesteel ball 68 is held at the terminal end of the transfer curve 62 b. Inthe slip mechanism 60, the steel ball 68 does not pass over the stepportion 62 a so that the inner bush 61 and the outer disk 62 rotatetogether when the torque is smaller than a preset value. As therotational torque exceeding the preset value is applied, the steel ball68 passes over the step portion 62 a, travels for a full circle alongthe inner periphery of the outer disk 62 with being pressed by thespring S and enters in the position at the terminal end again.

[0162]FIG. 26(b) shows a variation in which a spring S as a torquelimiter is compressed between a small-diameter inner bush 61 and anouter disk 62. As shown in this figure, the outer end of the spring S isinserted into a recess 62 d formed in the inner periphery of the outerdisk 62 and does not come off the recess 62 d with bending of the springcaused by torque less than a preset torque. Therefore, the inner bush 61and the outer disk 62 rotate together. As the rotational torque appliedexceeds a preset value, the outer end of the spring S slides along theinner periphery of the outer disk 62. After the terminal end slides fora full circle, the terminal end enters into the recess 62 d again.

[0163]FIG. 26(c) shows a slip mechanism 60 similar to that shown FIG.26(a). In this slip mechanism 60, an elastic ball 69 is employed. Theelastic ball 69 is deformed in the radial direction and pressed againstthe inner periphery of the outer disk 62 by pressure of the spring S. Asa rotational torque exceeding the preset value is developed between theinner bush 61 and the outer disk 62, the elastic ball 69 isshear-deformed to cancel the engagement between the inner bush 61 andthe outer disk 62, so that the inner bush 61 and the outer disk 62separately rotate.

[0164]FIG. 26(d) shows a variation of the slip mechanism shown in FIG.25(a). The flange of the outer disk 62 is clamped between two innerbushes 61 a and 61 b, wherein the distance between them can becontrolled by screws 61 c so as to obtain desired resistant torque. Ifnecessary, springs (not shown) may be attached to the screws 61 c forcontrolling the pressure on the disk of the inner bush 61.

[0165] Variations of the webbing withdrawal detecting unit 40 will bedescribed now. Instead of the fan-like switch plate 41 (see FIG. 8),variations of a switch detecting the webbing withdrawal are shown inFIGS. 27(a) and 27(b).

[0166]FIG. 27(a) shows a withdrawal detecting unit 40 comprising a ring46 provided with a trigger projection 46 a formed on the peripherythereof and a bush 45 which can rotate relative to the ring 46 with apredetermined resistance. The bush 45 directly rotates by the rotationof the spool (not shown). When the rotational torque is less than theresistance, the ring 46 rotates together with the bush 45. A limitswitch 44 is turned ON by the trigger projection 46 a. FIG. 27(b) showsa withdrawal detecting unit for turning ON the limit switch 44 in whicha ring-like spring 47 functioning as a cramping ring is fitted onto thebush 45, and the limit switch 44 is turned on by the integral rotationof the bush 45 and the spring 47 with the aid of friction between thebush 45 and the biasing force of the spring 47. Instead of theknown-type limit switch used in this embodiment, a normal contact switchmay be used. Further, a photodetector may be used. In this case, a slitis formed in a switch plate or a ring and the switch plate or the ringrotates so that the photodetector receives light passing through theslit. Alternatively, a proximity sensor of sensing metal which candetect the movement of a metallic switch plate or a metal ring or a Hallelement which can detect change in magnetic field may be used.

[0167] The spool rotation detecting unit will be described hereinafter.In the spool rotation detecting unit, instead of the aforementionedvariable resistor for directly detecting change in voltage, aphotodetector of encoder type, a photodetector for detecting theposition of the slit which can used also for the withdrawal detectingunit, a proximity sensor, or a magnetic detector for reading a positionby a magnetic head may be used.

[0168] Though the DC (direct current) motor is used as a motor in thisembodiment, various known servo motors which are variable speed motorsmay be used. For example, a stepping motor, an ultrasonic motor, an ACmotor may be used with a corresponding motor driving circuit, therebyachieving the winding operation as mentioned above. It is preferable bythe reason of wiring harness that the control circuit for driving themotor is positioned in a space below the webbing winding-up portioncreated when the motor is assembled in such a manner that the controlcircuit is disposed adjacent to the motor. However, the motor may bepositioned in any suitable place in a frame.

[0169] As described above, the present invention can provide seat beltwinding functions suitable for various conditions of the occupant. Thesefunctions are set at standard values in shipping from a factory. Anoccupant can simulate these modes (simulating function) so as to changethe effects of the functions to prefer degrees. This operation can beperformed by using a display of a navigation system installed in thevehicle or using an exclusive controller.

[0170] In addition to a function of providing alarm sounds and messagesin the warning mode and the pretensioning mode, a function of providingvarious sounds or displaying operation confirmation images may also beadded in the comfort mode, thereby improving the operation ability.

[0171] These settings may be made via harnesses arranged in the vehicleso that a driver's seat is set separately from other seats or all of theseats are set to the same. These settings for the respective seats maybe made through telecommunication lines. For example, the setting modeof the retractors for the respective seats can be set corresponding tocommands which are inputted by the driver or another occupant with theaforementioned display or a remote controller via telecommunicationlines using any known protocols. Data used for these settings mayinclude IDS for specifying the seats and commands for setting therespective modes (warning, holding, pause (waiting), releasing, childseat fixing).

[0172] As described above, a retractor of this invention can providesuitable states of winding up a webbing corresponding to variousconditions by controlling the state of a single motor having aspeed-reduction mechanism with high adaptability or by combination ofsuch a motor with a known retractor, thereby securely providing comfortand safety for an occupant.

[0173] While the invention has been explained with reference to thespecific embodiments of the invention, the explanation is illustrativeand the invention is limited only by the appended claims.

What is claimed is:
 1. A control method of a seat belt retractorcomprising: receiving at least one of signals selected from a statesignal showing a movement of an occupant wearing a seat belt and anexternal signal obtained from detecting means installed in a vehicleduring running thereof, and controlling a rotation of a spool for awebbing by switching a rotational torque of a motor to a predeterminedreduction ratio corresponding to at least one of the state signal andthe external signal, or controlling a driving state of the motor to apredetermined torque, to thereby wind the webbing on the spool.
 2. Acontrol method of a seat belt retractor as claimed in claim 1, whereinthe state signal includes a signal showing withdrawal of the webbingwhile the webbing is in a winding state, by which a rotation of themotor is stopped.
 3. A control method of a seat belt retractor asclaimed in claim 1, wherein the state signal includes a signal showingthat a tongue of the webbing is engaged with a buckle of the webbing, bywhich the motor is driven with such torque as to wind the webbing to fitthe webbing onto the occupant.
 4. A control method of a seat beltretractor as claimed in claim 3, wherein the state signal includes asignal showing that the fitting of the webbing is accomplished, by whichthe torque of the motor is reduced or driving of the motor is stopped.5. A control method of a seat belt retractor as claimed in claim 1,wherein the state signal includes a signal showing that withdrawal ofthe webbing is cancelled, by which the motor is started to restart awinding of the webbing.
 6. A control method of a seat belt retractor asclaimed in claim 1, wherein in a condition that a tongue of the seatbelt is engaged with a buckle of the seat belt, when the webbing iswithdrawn and stopped, winding of the webbing is started at a time ofinterruption of the withdrawal of the webbing, and after fitting thewebbing to the occupant, the torque of the motor is reduced or drivingof the motor is stopped.
 7. A control method of a seat belt retractor asclaimed in claim 6, wherein the torque of the motor for fitting thewebbing to the occupant is set lower than a torque of the motor forfitting the webbing to the occupant just after the tongue is engagedwith the buckle.
 8. A control method of a seat belt retractor as claimedin claim 1, wherein the state signal includes a signal showing that atongue of the webbing is disengaged from a buckle of the webbing, bywhich the motor is activated to wind the webbing into the retractor. 9.A control method of a seat belt retractor as claimed in claim 1, whereinat a same time of or after a predetermined period of time from detectionof the withdrawal of the webbing, a power source of a control circuitfor operating the motor is turned ON.
 10. A control method of a seatbelt retractor as claimed in claim 1, wherein upon detection of asituation that the winding of the webbing is accomplished or that thewebbing has not been withdrawn for a predetermined period of time, apower source of a control circuit for operating the motor is turned OFF.11. A control method of a seat belt retractor as claimed in claim 1,further comprising: after a predetermined time from accomplishment ofwinding of the webbing, determining whether the winding of the webbingis needed, and winding the webbing if necessary.
 12. A control method ofa seat belt retractor as claimed in claim 1, wherein a speed of themotor is controlled to change the speed of winding of the webbing by themotor.
 13. A control method of a seat belt retractor as claimed in claim1, wherein the torque of the motor is switched to a preset value or avariable value by switching means according to the external signal towind the webbing by the motor.
 14. A control method of a seat beltretractor as claimed in claim 13, wherein the motor is controlled in amode in which the switching means is not released, to hold a drivingstate of the motor after being switched.
 15. A control method of a seatbelt retractor as claimed in claim 13, wherein the motor is controlledin a mode in which the switching means is not released, to hold adriving state of the motor after being switched through torque resistormeans of a speed-reduction mechanism.
 16. A control method of a seatbelt retractor as claimed in claim 15, wherein said mode is a holdingmode during running of the vehicle or a child seat fixing mode.
 17. Acontrol method of a seat belt retractor as claimed in claim 13, furthercomprising: transmitting a command signal of the motor corresponding tothe external signal to at least one of the seat belt retractorsinstalled in vehicle seats in a communicating method capable ofrecognizing the seats for mode setting of the vehicle seats.